<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        #f{
            width: 100px;
            height: 200px;
            background-color: red;
            border-radius: 5px;
        }
    </style>
</head>
<body>
<div id="f">

</div>
<button id="b">变形</button>
</body>
</html>
<script !src="">
    var b=document.getElementById("b")
//     b.onclick=function (){
// let f=document.getElementById("f")
//         // f.style="border-radius: 5px;"
//         // f.setAttribute("style","border-radius: 50px;")
//
//     }
b.addEventListener("click",function (){
    let f=document.getElementById("f")
    f.style="border-radius: 55px;"
})
</script>